The present invention relates to a composite apparatus for the direct projection and overhead or back-projection of slides.
Heretofore known apparatus for the direct projection of slides generally comprise a base on which is mounted the box of the projector, in which box is housed a source of light and which bears a lens. The slides having to be projected are generally contained in magazines in the form of rotating or sliding baskets, each slide to be projected being driven from the basket which contains it by transversely moving push element, to be taken to a position located between the source of light and the lens, and then to be returned into the basket, after projection, by a reverse movement of the transverse push element.
These apparatus for the direct projection of slides which are very wide-spread at the present time, present the drawback of requiring, for the direct projection of slides, the positioning of an independent screen, which must be unwound vertically in front of the lens. The owner of a slide projector must therefore possess an independent screen hence problems of bulk, storage and convenience of use. In fact, the fact of having to bring out an unwindable screen from where it is stored and of having to unwind it is an inconvenient operation, and owners of slide projectors consequently use them rarely in practice.
Certain known apparatus, such as those described in U.S. Pat. Nos. 3,885,868; 4,163,610 and DE Pat. No. 3029195, are equipped with an overhead or back-projection screen made of frosted glass, and with a mobile mirror adapted to occupy two positions, namely a position for direct projection in which the mirror is spaced apart with respect to the lens, aside or above said lens, to allow emergence of the light beam for direct projection, and an overhead of back-projection in which it is interposed immediately in front of the lens.
However, the apparatus according to U.S. Pat. Nos. 3,885,868 and 4,163,610 present the drawback of being cumbersome in height and of having a relatively complex internal structure, with three mirrors for reflecting the light beam. As to the apparatus according to DE Pat. No. 3,029,195, it ensures a projection on a frosted screen of small dimensions provided in a lateral wall of the box, when the mirror is placed in front of the lens, and in that case it merely performs the role of a viewer and not that of an overhead or back-projection apparatus producing an image of large-dimensions which may be oberved by several persons. Finally, all the heretofore known composite apparatus ensure back-projection of the image either on the front face or on a lateral face of the box, so that, if it is desired during projection to pass from observation on a remote large screen to observation on the frosted screen of the projector, the observers must move with respect to the apparatus.